Electromechanical clamping device

Abstract

An electromechanical clamping device with hydraulic assistance. A thrust mechanism driven by an electric motor displaces two clamping jaws with respect to each other along a guide device. One clamping jaw is divided into two mutually displaceable part java. A chamber to hold pressure medium is formed between the part jaws. The first part jaw can be displaced along the guide device and locked with respect to the latter. One part jaw is provided with a first cylinder coupled to the output of the thrust mechanism. In order to close the clamping device, in a first step the thrust mechanism pulls the part jaws against the other clamping jaw, and in a second step the thrust mechanism delivers pressure medium from the first cylinder into the chamber between the two part jaws, with the first part jaw locked with respect to the guide device. To open the clamping device, in a first step a second cylinder arranged between the two part jaws pulls the part jaws against each other, with the first part jaw locked with respect to the guide device, and then in a second step the thrust mechanism forces the part jaw coupled to it in the opening direction, forcing the other part jaw with it, with the first part jaw unlocked from the guide device. The clamping device is provided for production machines, in particular for injection molding machines.

1. An electromechanical clamping device with hydraulic assistance for a production machine, in particular for an injection molding machine, the device comprising:
 two clamping jaws ( 11 ,  13 ) on which in each case a part mold ( 21 ,  22 ) of a divided mold ( 23 ) is held,  
 one ( 11 ) of the clamping jaws is fixed and the other ( 13 ) of the clamping jaws is arranged such that it is displaceable with respect to the one clamping jaw,  
 a thrust mechanism ( 26 ) driven by an electric motor ( 25 ) moves the displaceable clamping jaw ( 13 ) along a guide device ( 12 ),  
 the displaceable clamping jaw ( 13 ) is divided into two part jaws ( 16 ,  17 ), displaceable with respect to each other in a direction of the guide device ( 12 ) and a chamber ( 20 ) to hold pressure medium is formed between the part jaws ( 16 ,  17 ),  
 the first part jaw ( 16 ) is displaceable along the guide device ( 12 ) and is lockable with respect to the latter,  
 one ( 17 ) of the two part jaws is provided with a first cylinder ( 33 ), a piston ( 32 ) of which is coupled to output ( 27 ) of the thrust mechanism ( 26 ),  
 in a closing operation in order to close the clamping device, in a first step the thrust mechanism ( 26 ) pulls the part jaw ( 17 ) coupled thereto against the fixed clamping jaw ( 11 ), pulling the other part jaw ( 16 ) therewith, in a second step the thrust mechanism ( 26 ) delivers pressure medium from the first cylinder ( 33 ) into the chamber ( 20 ) between the two part jaws ( 16 ,  17 ), with the first part jaw ( 16 ) locked with respect to the guide device ( 12 ),  
 in an opening operation in order to open the clamping device, in a first step a second cylinder ( 41 ) arranged between the two part jaws ( 16 ,  17 ) pulls the second part jaw ( 17 ) against the first part jaw ( 16 ), with the first part jaw ( 16 ) locked with respect to the guide device ( 12 ) and the chamber ( 20 ) between the part jaws ( 16 ,  17 ) relieved of pressure; after the mold ( 23 ) has been opened, in a second step the thrust mechanism ( 26 ) forces the part jaw ( 17 ) coupled thereto in opening direction, forcing the first part jaw ( 16 ) therewith with the first part jaw ( 16 ) unlocked from the guide device ( 12 ).  
 
   
   
     2. The clamping device as claimed in  claim 1 , wherein the part jaws ( 16 ,  17 ) are spaced apart from each other when the clamping device is closed. 
   
   
     3. The clamping device as claimed in  claim 2 , wherein a control loop is provided which keeps distance between the two part jaws ( 16 ,  17 ) constant during the first step in the closing operation. 
   
   
     4. The clamping device as claimed in  claim 2 , wherein the guide device ( 12 ) is provided with a latching division, with which a latching device ( 15 ) held on the first part jaw ( 16 ) interacts. 
   
   
     5. The clamping device as claimed in  claim 2 , wherein the second cylinder ( 41 ) is enabled to have pressure medium applied thereto in the first step of the opening operation such that distance between the two part jaws ( 16 ,  17 ) decreases. 
   
   
     6. The clamping device as claimed in  claim 5 , wherein the thrust mechanism ( 26 ) assists the opening operation, application of pressure medium to the second cylinder ( 41 ) being controlled such that force exerted on the second part jaw ( 17 ) by the thrust mechanism ( 26 ) does not exceed a predefinable threshold value (i Ma ). 
   
   
     7. The clamping device as claimed in  claim 6 , wherein current (i Mi ) drawn by the electric motor ( 25 ) is supplied to a force controller ( 78 ) as the actual value of the force exerted on the second part jaw ( 17 ) by the thrust mechanism ( 26 ), and wherein a force controller ( 78 ) is supplied with the predefinable threshold value (i Ma ) as a desired value for said force. 
   
   
     8. The clamping device as claimed in  claim 7 , wherein control difference (x di ) formed from the actual value of the current (i Mi ) drawn by the electric motor ( 25 ) and the predefinable threshold value (i Ma ) has superimposed thereon time derivative of pressure (p i ) applied to a piston ( 46 ) of the second cylinder ( 41 ). 
   
   
     9. The clamping device as claimed in  claim 7 , wherein position (x i ) of a piston ( 46 ) of the second cylinder ( 41 ) is supplied to a position controller ( 81 ) as actual value of the distance between the two part jaws ( 16 ,  17 ), and wherein the position controller ( 81 ) is supplied with a desired value (x s ) that determines the distance between the two part jaws ( 16 ,  17 ). 
   
   
     10. The clamping device as claimed in  claim 9 , wherein an actuating signal (y x ) from the position controller ( 81 ) is supplied to a hydraulic control device ( 53 ) if the current (i Mi ) drawn by the electric motor ( 25 ) is less than a second threshold value (i Mu ), and wherein the hydraulic control device ( 53 ) is supplied with actuating signal (y K ) from the force controller ( 78 ) if the current (i Mi ) drawn by the electric motor ( 25 ) is greater than the second threshold value (i Mu ), the second threshold value (i Mu ) being chosen such that it lies between the maximum current required to move a clamping jaw ( 13 ) and first-mentioned threshold value (i Ma ). 
   
   
     11. The clamping device as claimed in  claim 10 , further comprising a neutral position of the hydraulic control device ( 53 ) in which chambers ( 40 ,  47 ) of the second cylinder ( 41 ) are connected to each other via restrictors and to a pump ( 54 ) and tank ( 43 ). 
   
   
     12. The clamping device as claimed in  claim 11 , further comprising a changeover device ( 83 ) which supplies the second hydraulic control device ( 53 ) with actuating signal (y x ) from the position controller ( 81 ), the actuating signal (y K ) from the force controller ( 79 ) or a constant actuating signal (y v10 ) for neutral position. 
   
   
     13. The clamping device as claimed in  claim 1 , further comprising a machine control system ( 70 ) which controls the individual steps in working sequence of a production machine. 
   
   
     14. The clamping device as claimed in  claim 13 , wherein parameters and desired values required for control of the working sequence of the production machine are stored in the machine control system ( 70 ). 
   
   
     15. The clamping device as claimed in  claim 1 , wherein the first cylinder is a double-ended cylinder ( 33 ), whose piston rod ( 34 ) facing away from the thrust mechanism ( 26 ) penetrates into a further chamber ( 35 ), wherein the further chamber ( 35 ) is connected via a first nonreturn valve ( 36 ) to a chamber ( 40 ) of the second cylinder ( 41 ), and the further chamber ( 35 ) of the double-ended cylinder ( 33 ) is connected via a replenishing valve ( 42 ) to a tank ( 43 ).